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Trouble Shooter

Tires usually offer tens of thousands of miles of trouble-free service. But before the tread has worn to the wear bars, other factors may provide legitimate reasons for removing some tires from service.

Tired Out

Bob Cerullo’s column in last month’s Motor got me thinking about tires. While Bob wrote about the dangers of inadequately torqued wheel fasteners and the very real hazard of wheel and tire assemblies coming off a vehicle, I’ve been thinking about a tire safety issue at the other end of the spectrum. There comes a time when some tires should be removed from a vehicle, preferably by a professional, before they can do real harm to the vehicle owner or others he may come in contact with.

All of us have learned how to spot a tire that has reached the end of its useful life due to tread wear. Tread wear gauges, as well as the tire’s built-in wear bars, can be used to quickly determine whether a tire does or does not have a sufficient amount of remaining tread to stay in service. Irregular tread wear due to alignment problems as well as over- or underinflation also can be quickly identified with a visual inspection.

On vehicles that do not receive regular use, the tire identification number (TIN) is another quick way to determine a tire’s suitability for continued use. Since 2000, all passenger car tires must have a TIN that includes the tire’s date of manufacture in its last four digits. If the vehicle is a collector car or motor home that has been sitting for months or years without being driven, the TIN may be a good place to start. The vehicle’s tires may look good, with plenty of remaining tread, but the tires’ advanced age may have caused them to deteriorate in ways that are difficult to see or gauge by conventional methods.

Other tires that may look good but are in fact bad are those that have been stored off the vehicle for an indefinite period. As I’m writing this, the air temperature has already started to cool and it won’t be long before we’ll be thinking about snow and snow tires. If your shop is in an area that receives significant snowfall, some of your customers will likely be bringing in snow tires they hope to get “just one more season” out of. There are many things to consider before accepting a request to remount such tires and return them to service.

How were those snow tires stored? Stored tires should be protected against environmental effects such as sunlight, high heat, ozone and other potentially damaging conditions. Ideally, tires should be stored in an area that’s clean, dry and well ventilated, but with a minimum of circulating air. The storage area should be shaded or dark, with mild ambient temperature conditions. The stored tires should be raised off the floor to minimize exposure to moisture or damage, and contact with petroleum-based products and/or other volatile solvents or substances should be avoided. Tires also should be stored away from electric motors, battery chargers, generators, welding equipment or other ozone-generating sources. If your customers are storing their snow tires in a typical home garage, it’s unlikely that all of these storage recommendations are being followed.

Even if they’re not being improperly stored, tires are subjected to a very harsh environment while they’re on the vehicle. They’re stretched millions of times as they roll over rough, uneven roads, and they’re exposed to acid rain, brake dust, harsh chemicals and direct sunlight, as well as summer’s heat and winter’s cold. Rubber compounds include antiaging chemicals, but exposure to the elements will eventually cause the tire’s rubber to lose some of its elasticity and allow surface cracks to appear.

These small surface cracks go by several different names, including weather checking, weather cracking and ozone cracking, and they typically develop in the sidewalls or at the base of the tread grooves. They may be cosmetic in nature if they don’t extend past the rubber’s outer surface, or may be a reason to replace the tire if they reach deep into the rubber.

Many things can cause these cracks, including several I’ve already listed under tire storage guidelines. Cracking can be accelerated by exposure to heat, vehicle exhaust, ozone and sunlight. Some sidewall cracking has been linked to curb abrasion or the excessive use of tire cleaners or dressings. These dressings may remove some of the tire’s antioxidants and antiozone protection during every cleaning procedure.

The antiaging chemicals used in the rubber compounds are more effective when the tire is “exercised” on a regular basis. The repeated stretching of the rubber compound helps resist cracks forming. Tires on vehicles that are driven infrequently or that accumulate low annual mileage are more likely to experience cracking because long periods of storage interrupt “working” the rubber.

No industry standard has been established to determine when a tire has too many small cracks for a given sidewall area or if the cracks are deep enough to warrant tire replacement. One tire manufacturer recommends replacement if the cracks are more than 2⁄32 in. deep or if internal tire components are visible. Like drive belts, your experience may be your best guide in making a determination. Some tire manufacturers will make an adjustment under warranty if the cracks appear within a certain period after the tires were purchased.

There are several excellent sources for additional information about tire wear, service and maintenance. The Tire Industry Association (www.tireindustry.org) publishes the Passenger and Light Truck Tire Conditions Manual. The Rubber Manufacturers Association offers Care and Service of Passenger and Light Truck Tires, which is available for download on its website (www.betiresmart.org). Tire Rack, one of the largest online retailers of wheels and tires, offers several informative articles on tires and tire wear on its website (www.tirerack.com).